In the original mining of coal, mountains of coal fines are developed from the operation and after separation are often submerged in water and in open pits as refuse, gob, or tailings. In general, before the "energy crunch" little effort had been made to recover the energy available in such coal mine tailings for costs of recovery in useful form were not economically promising. Of course, newly mined coal can be crushed to useful size as well, and coke particles are not precluded.
Heretofore solid blocks and "logs" of processed coal have been prepared in compressed package form utilizing various qualities of binders, primarily waste tars, bitumens, etc., by compression under high pressures into a form. So far as presently known, the continuous extrusion of wet coal (5-20% moisture level) with a water soluble binder has not been reduced to commercial practice. Forming useful "logs" or "blocks" of particulate coal by "water wetted" extrusion has not heretofor been known to be commercially successful.
Heretofore solid blocks and "logs" of processed coal in packaged form have been made available, but because of the quantities of water essentially present for mixing and forming, the formed blocks required a subsequent drying operation which itself required considerable energy input.
Further, in producing the coal mixtures a variety of binders have been used. In general organic solvent soluble binders failed to "wet" the coal particles and high temperatures and pressures were resorted to in individual molding operations to produce briquetted coal-particle integration. One patentee refers, for example, to pressures of from 50--800 atmospheres. Another used butadiene acrylonitrile polymers to bind the blocks at temperatures of about 230.degree. C.
Schultz, U.S. Pat. No. 2,531,828 illustrates vertical and horizontal bores through fuel blocks which are sealed over with an impervious (paper) coating. Schultz provides no air and flame passageway through the base of his block or a capacity to use plural blocks in a nesting arrangement to obtain a coke forming effect during combustion.
So far as applicants are aware, the prior art also does not provide an extrudable coal, water-binder, solvent mixture which cohesively holds together at room temperatures and extruding pressures. The present invention provides an extruded product which has sufficient integrity to maintain its geometric, cross-sectioned regularity to permit both longitudinal and vertical drilling, slotting, cutting, and forming operations upon the freshly extruded coal mixture without a prior intermediate drying step.
It is a principal objective of this invention to provide a first plastic extrudable mixture, the major proportion by weight thereof being a partially dried or inspissated coal particle of about 10 to about 100 screen mesh size and where the water has been largely removed by both mechanical and evaporation removal steps. The divided coal and coal-derived particles are thoroughly mixed with minor proportions of additives thereto. The essential additives to the water wetted coal include an appreciable amount of a macroscopic particulate mass of finely divided combustible organic waste material which may originate from both natural and synthetic sources. A common characteristic of these organic wastes is their fibrous nature. Principally illustrative of those of natural origin are shredded waste paper and agricultural by-products illustrated by the cellulosic fiber wastes, i.e. "straw" and the heavier stalks, illustratively from corn and sugar cane (bagasse).
The synthetic fibers include as illustrative the polymeric fibers of polyolefins which because of their fine capillary thread-like quality and preferentially oil-wetted surfaces retain a relatively large quantity of lipophilic material, such as the common liquid hydrocarbon distillates commonly used for fuel purposes in the natural capillaries formed from macroscopic clumps or packets of the said fibers in close proximity to one another.
The foregoing are employed to retain and hold a companion ingredient; namely, a combustible (liquid) hydrocarbon fraction within these capillary fibrous masses.
A further essential additive is a selected methyl cellulose product which serves to take up extraneous water present in the major particulate coal particle component. While the amount of the water-soluble methyl cellulose is not critical, the quality of the water soluble alkyl cellulose has been found to be critical to the success or failure of the solid fuel particle extrusion step. The quality of the methyl cellulose in the Examples shown herein has been found to be extremely useful, whereas a number of other qualities, the nature of which is not available in sufficient detail to be able to define by known physical and chemical properties, can be the source of many problems in the mechanical act of producing successful particulate coal and coke extrusions as are herein disclosed.
When appropriate grades of methyl cellulose are used in the quantities indicated in the Examples, fuel particle extrusions can be produced at room temperatures to produce a longitudinal extrudate in a pre-formed geometrical dimensional mass which can be cut, drilled and/or slotted to produce the essential flues without losing the integrity of the extruded geometric form.
The entire block after completion of the air passageways by cutting, drilling, slotting or extrusion is preferably dipped in a liquid hydrocarbon distillate thereby to sorb the more volatile solvent to aid initial ignition. Thereafter, the block is substantially over-coated with a molten combustible coating having a melting point above about 100.degree. F. but less than about 225.degree. F., preferably a mineral wax.